Take a look at sambapos.org
That is the forum for V3, although very few people will still be using it. You are likely to get much better support for V4 (although that is also reducing). Many of us are using V5 which is free to try and only $99 for life if you decide to purchase it.
The $99 covers your entire deployment, there is no restriction on how many terminals or printers you have attached to the same database.
V5 offers so many powerful options, for the sake of $99 it’s difficult to argue a case for trying to develop for V3